title: Trophic cascades: linking ungulates to shrub-dependent birds and butterflies.
abstract: 1. Studies demonstrating trophic cascades through the loss of top-down regulatory processes in productive and biologically diverse terrestrial ecosystems are limited. 2. Elk Island National Park, Alberta and surrounding protected areas have a wide range of ungulate density due to the functional loss of top predators, management for high ungulate numbers and variable hunting pressure. This provides an ideal setting for studying the effects of hyper-abundant ungulates on vegetation and shrub-dependent bird and butterfly species. 3. To examine the cascading effects of high ungulate density, we quantified vegetation characteristics and abundances of yellow warbler Dendroica petechia and Canadian tiger swallowtail Papilio canadensis under different ungulate density in and around Elk Island National Park. 4. Using Structural Equation Models we found that ungulate density was inversely related to shrub cover, whereas shrub cover was positively related to yellow warbler abundance. In addition, chokecherry Prunus virginiana abundance was inversely related to browse impact but positively related to P. canadensis abundance. 5. These results demonstrate a cascade resulting from hyper-abundant ungulates on yellow warblers and Canadian tiger swallowtails through reductions in shrub cover and larval host plant density. The combined effect of the functional loss of top predators and management strategies that maintain high ungulate numbers can decouple top-down regulation of productive temperate ecosystems.
authors.affiliation: Department of Biological Sciences, Biological Sciences Building, University of Alberta, Edmonton, AB, Canada T6G 2E9.
authors.forename: Kristine
authors.initials: K
authors.lastname: J Teichman
authors.forename: Scott E
authors.initials: SE
authors.lastname: Nielsen
authors.forename: Jens
authors.initials: J
authors.lastname: Roland
mesh_terms: D000416:Alberta; D000818:Animals; D002080:Butterflies / Q000502:physiology*; D017753:Ecosystem; D020387:Food Chain; D011156:Population Density; D012418:Ruminants / Q000502:physiology*; D020308:Songbirds / Q000502:physiology*
keywords: Dendroica petechia; Papilio canadensis; ecosystem; terrestrial; top‐down regulation